FIG. 1A shows a conventional trench MOSFET 100 of prior art, wherein a single trenched source-body contact 101 is penetrating through an n+ source region 102 and extending into a P body region 103 between two adjacent trenched gates 104 in an active area, wherein the n+ source region 102 is formed in an upper portion of the P body region 103. For trench MOSFET like the trench MOSFET 100 with voltage rating below 100V (Low Voltage), channel resistance Rch accounts for about 10% and 30% of total Rds at Vgs=10V and at Vgs=4.5V respectively for a 30V N-channel device. It can be seen that the channel resistance Rch plays an important role in on-resistance, especially at Vgs=4.5V. Therefore, the smaller pitch of the device, the lower Rds. So far, the minimum 1.0 um pitch is achieved by using 0.18 um and tungsten plug technologies for a cell density around 500 M/in2. However, for voltage rating beyond 100V (Middle and High Voltages), applications of the middle and high voltage devices are more at Vgs=10V. The Rch is less than 10% of Rds. For trench MOSFETs having device structure as shown in FIG. 1A, no much improvement in Rds but significant increase in gate charge with higher cell density.
Another prior art U.S. Pat. No. 8,049,273 discloses a device structure 110 having multiple trenched source-body contacts 111 in unit cells for improving the peak induced voltage in switching converter, as shown in FIG. 1B. However, n+ source regions 112 are disposed not only along channel regions but also among the multiple trenched source-body contacts 111, causing poor avalanche capability issue because two additional parasitic n+/P/N+ bipolar transistors exist in the device structure 110.
Therefore, there is still a need in the art of the semiconductor power device, particularly for trench MOSFET design and fabrication, to provide a novel cell structure, device configuration that would resolve these difficulties and design limitations.